Oceans 4Ever

Hello, Sharktakular readers!

I’m Emily Fisher, online editor at the ocean conservation organization Oceana, and I wanted to share with you one of my favorite things from our website so far this year — and it happens to be about sharks.

I interviewed shark biologist Michelle McComb of Florida Atlantic University for the latest issue of our magazine. She made big news late last year for her work on a study that begins to answer a fundamental question: why are hammerhead sharks shaped the way they are?

McComb and her fellow researchers found surprising results about hammerhead vision. (And I learned a million-dollar word — a hammerhead’s funny head shape is known scientifically as a “cephalofoil.”)

EF: What did you and your colleagues discover about hammerhead vision?

MM: The popular literature is filled with claims that hammerheads have better vision, but this was never tested. Our goal was to quantify the extent of the visual fields of hammerhead sharks in contrast to more typical-shaped sharks, in order to determine if they possessed binocular vision.

What we found was a surprise – hammerhead sharks do have binocular vision, and even more surprising, the extent of binocular overlaps was greater than found in the typical-shaped sharks.

When we originally discussed this project we thought we were setting out to dispel the myth that hammerheads possessed binocular vision. We had no idea that hammerheads would have even larger binocular overlaps than normal sharks! 

EF: Why is it significant that hammerheads have binocular vision?

MM: Binocular vision evolved to facilitate depth perception. Each eye sees a slightly different image and it’s the subtle differences within these images that are used for depth cues. So the wider separation of the eyes in hammerhead sharks enhances the stereoscopic effect and depth perception. This translates into a visual advantage for a predator like the hammerhead shark in its ability to accurately judge the distance of moving objects like prey.

EF: As a result of your team’s research, do we have a definitive answer for why hammerhead shark heads are shaped the way they are?

MM: Our results support the idea that vision may have played a role in the evolution of the hammerhead. However, there are several other hypotheses that remain, some of which are untested.

It is possible that several factors in combination may have led to the evolution of the head shape, including the following hypotheses:

1. The head acts as a bow plane to provide hydrodynamic lift during swimming.

2. Possible enhanced electrosensory ability due to the larger size of the head and the potential for possession of more electrosensors in the head.

3. Enhanced olfactory ability due to the wide separation of the olfactory organs and naris (nostrils) on the head.

4. The head shape may help hammerheads pin down prey items like stingrays. However, this is not strongly supported because the diet of many hammerhead species (there are 8 species of hammerhead) does not include stingrays.

EF: The media response to your research was huge.  Why do you think people were so interested in it? What do you hope people came away with after reading about it?

MM: I think people enjoy sharks because they are mysterious and there is so much about them we still do not know.  I hope people understand that hammerheads are the most recently evolved sharks in the ocean and we have demonstrated that their visual abilities have been enhanced as a result of their strange expanded head.

EF: Have you ever swum with sharks? If not, do you want to?

MM: I have had the pleasure of travelling to a lot of different countries over the world and I have had the privilege of swimming with many sharks species.  I have swam with great white shark off the coast of South Africa, bull sharks in Australia, hammerheads in Hawaii, lemon sharks in Florida, and Caribbean reef sharks in the Bahamas.  Every time I see a shark while I am in the water I get a thrill and I feel so lucky and humbled that I am sharing space with them.

EF: What do you think is the biggest problem facing sharks today? Why is it important for humans to protect them?

MM: The cruel and wasteful practice of shark finning is the biggest threat to shark populations worldwide.  Over 100 million sharks are killed each year for their fins which are dried and used to make shark fin soup, a flavorless broth, which is an Asian delicacy and status symbol.

This overharvest is unsustainable since sharks reproduce and grow slowly. The oceans are vital to life on our planet and sharks have been in the oceans for 400 million years, playing a pivotal role in ecosystem balance.